Field of the Invention
This invention relates to a touch panel inputting device. More specifically, this invention relates to a touch panel inputting device which detects the contact of an operation body on an operation surface, based on light blocking in a scanning light path plane.
Description of the Related Art
A generic image forming apparatus, for example MFP (Multifunction Peripheral), is equipped with an operation panel. The operation panel has a display panel which displays an operation screen including software keys, and a touch panel inputting device placed on the display panel. The image forming apparatus detects touches on software keys etc. displayed on the display panel, by using the touch panel inputting device. The image forming apparatus executes a process assigned to the touched key etc. at the location where the touch is detected. Herewith, the user can perform an operation such as a setting for devices, by touching the operation screen displayed on the display panel. The user can perform instinctive operations and enjoy good operability.
Touch panel inputting devices can detect touches by various methods, for example an optical type method, a resistive type method, a capacitance type method, or the like. Here, a touch panel inputting device which adopts an optical type method will be explained.
FIG. 27 schematically shows a structure of a conventional optical touch panel inputting device. FIG. 28 schematically shows a scanning light path plane of the conventional optical touch panel inputting device.
Referring to FIGS. 27 and 28, the conventional touch panel inputting device comprises a pair of light emitting elements array 1101 and light reception elements array 1102 which are placed at both end portions of the X-axis on operation surface CP of display panel 1100, facing each other. Further, a pair of a light emitting elements array and a light reception elements array facing each other is placed at both end portions of the Y-axis on operation surface CP of display panel 1100. The light emitting elements array is configured with a plurality of LEDs (Light Emitting Diodes). The light reception elements array is configured with a plurality of PDs (Photodiodes).
The optical touch panel inputting device receives light emitted from each of LEDs at each of PDs to scan operation surface CP. The optical touch panel inputting device determines the touched position, based on the location of the PD at which the light receiving amount is reduced. According to the conventional optical touch panel inputting device, the installation heights of all LEDs and PDs is same (distances between operation surface CP and each of LEDs and PDs is same). Hence, scanning light path plane SL101 is configured parallel with operation surface CP. Scanning light path plane SL101 is close to operation surface CP.
According to an optical touch panel inputting device, it is structurally easy to manufacture a big panel. Further, an optical touch panel inputting device is heavy-duty, since users do not touch the sensors directly. On the other hand, an optical touch panel inputting device has a problem of tendency to misdetect foreign material adhered to the operation surface as touch input.
To prevent the misdetection of foreign material adhered to the operation surface as touch input, a conventional optical touch panel inputting device performs the following behavior. The optical touch panel inputting device detects light blocking when the light receiving amount of the PD is reduced. The optical touch panel inputting device calculates the size of the area where light is blocked (a light blocking area), based on the locations of the PDs at which the light receiving amount is reduced. The optical touch panel inputting device recognizes the light blocking as a touch, when the calculated light blocking area is more than a threshold value of a light blocking area. The optical touch panel inputting device does not recognize the light blocking as a touch, when the calculated light blocking area is less than the threshold value of a light blocking area. In this case, the optical touch panel inputting device recognizes that light was blocked by foreign material.
The technique of a conventional optical touch panel inputting device is disclosed in Document 1 (Japan Patent Publication No. 2010-181916). The optical touch panel inputting device of Document 1 comprises an operation unit, a calculation unit for detecting adhesives of particles, dust, or the like on the operation surface based on the detection result of the operation unit, and an operation surface movement for moving the operation surface in Z-axis direction, perpendicular to the operation surface. The operation unit is for detecting X and Y coordinates of the point on the operation surface by detecting light blocking in matrix optical axes formed by pairs of light emitting elements and light reception elements. The calculation unit determines that there is an adhesive on the operation screen, in case that the area of light blocking is less than a prescribed threshold value. The calculation unit eliminates the effect of the adhesive, by moving the operation surface in Z-axis direction using the operation surface movement.
According to the conventional optical touch panel inputting device, a touch performed by a fingertip of a user may not be detected. Then, the conventional optical touch panel inputting device has a problem that responsiveness of operations is not good.
FIG. 29 shows the relationship among an operation state of a finger, a contact area of the finger and contact determination, in accordance with a conventional optical touch panel inputting device.
Referring to FIG. 29, when a user touches operation surface CP by the ball of a finger, as shown in (a), the light of a lot of scanning light paths in scanning light path plane SL101 is blocked by the finger. Then, the light receiving amount is reduced at a lot of the PDs, and the calculated light blocking area is large. In consequence, since the light blocking area is more than threshold value T2 of a light blocking area, a touch is detected. On the other hand, when a user touches operation surface CP by the fingertip, as shown in (b), the light of a few scanning light paths in scanning light path plane SL 101 is blocked by the finger. Then, the light receiving amount is reduced at only a few PDs, and the calculated light blocking area is small. In consequence, since the light blocking area is less than threshold value T2 of a light blocking area, a touch is not detected.
To increase the light blocking area calculated when a user touches operation surface CP by a fingertip; one idea is that scanning light path plane SL 101 is placed at the location away from operation surface CP. However, in accordance this idea, a touch may be detected before the finger reaches operation surface CP. Further, an amount of displacement resulted from parallax between the detected position and the touched position may be large, in case that the user looks at operation surface CP at an angle.
In case that the operation surface slopes and a user touches a front side of the operation surface, the user tends to use a fingertip.
FIG. 30 schematically shows the relationship between a point of the operation and the contact area, in case that operation surface CP is fixed at constant height and a constant angle.
Referring to FIG. 30, an operation surface of a MFP etc. is fixed to the main body of the apparatus unlike a portable terminal device, so that the surface slopes with respect to the horizontal plane. When operating such the operation panel, a user performs touching on the operation surface, not moving the wrist as a supporting point broadly but changing only the direction of the finger. More specifically, as shown in FIG. 30(a), a user tends to use the ball of a finger when touching an upper part of operation surface CP. As shown in FIG. 30(b), a user tends to use the fingertip when touching a lower part of operation surface CP. Hence, in case that the touching point is lower on operation surface CP, the light blocking area is smaller and a margin with respect to a threshold value of a light blocking area is narrower. In consequence, a touch may be less detectable depending on the touch location, although the user touches the operation surface at constant strength. Hence, responsiveness of operations worsens.
The object of this invention is to provide a touch panel inputting device having good responsiveness of operations.